This invention relates to improved stop circuits for rebalanceable servo systems and particularly to systems of the type that are used in null balance recorders wherein the position of a pen and pointer combination is varied in accordance with the magnitude of an input signal.
In general the prior art has employed stop circuits in servo systems of this type in which the error signal amplifier, or its counterpart, was disconnected from the balancing motor or in some other way was made inoperative to control the balancing motor. Inherent in such a system is the problem that when the servo system is returned to its normal operating condition the balancing motor then operates at its full speed capability to restore the servo system to balance. Such high speed operation is undesirable as it may result in undesirable overshooting of the balance point. With the present invention such problems are avoided by maintaining the error signal at substantially zero throughout the period that the servo system is stopped. By virtue of a feedback connection from the error amplifier output to the integrating amplifier the error signal is restricted to a predetermined rate of change when the servo system is returned to its normal operating condition. While this invention has utility in positional type servo systems in general it finds particular utility in rebalanceable servo systems used with rebalanceable graph marking recorders and particularly with high speed multipoint industrial recorders wherein the servo system must be periodically interrupted or placed into a stopped condition during the time that the data for a particular point is being printed on the recorder chart in avoidance of smearing of the printed point.
It is thus an object of this invention to provide a stop circuit for a positional rebalanceable servo system that limits the rate at which the system is restored to balance after its operation has been interrupted by a stop circuit.
It is a further object of this invention to limit the rebalancing rate of the servo system to a preselected rate.